Olmesartan medoxomil is the name commonly given to (5-methyl-2-oxo-1,3-dioxol-4-yl)methyl 1-((2′-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl)-4-(2-hydroxypropan-2-yl)-2-propyl-1H-imidazole-5-carboxylate, shown as (1) below. This chemical is known as an antagonist of angiotensin-II receptors and acts as an antihypertensive agent.

According to an article in J. Med. Chem, 1996, 39, 323-338 titled Nonpeptide Angiotensin II Receptor Antagonists, by Yanagisawa et al, olmesartan medoxomil is prepared as shown in the Scheme 2 below from the tritylated intermediate (2) by hydrolysis in aqueous acetic acid at elevated temperature in which triphenylmethanol is released.

However, continued exposure to acidic conditions and the presence of water may lead to the cleavage of the ester bond to give olmesartan acid (3), as shown below (Scheme 3).

In addition to this degradation compound, the tritylated intermediate (2) would also contain impurities from previous steps.
WO 2007/017135 also discloses a method of making olmesartan medoxomil. In this method, the tritylated intermediate (2 as shown in scheme 2 above) is dissolved in acidic solution which causes deprotection to occur. The solution is then neutralised and olmesartan medoxomil is precipitated. The crude precipitated olmesartan medoxomil is then recrystallised to purify it.
There remains the need for an efficient way of preparing olmesartan medoxomil of high purity.